The subject matter disclosed herein relates to reciprocating engines and, more specifically, to detecting changes (e.g., increases or rises) in compression ratio and peak firing pressure using a knock sensor.
Combustion engines typically combust a carbonaceous fuel, such as natural gas, gasoline, diesel, and the like, and use the corresponding expansion of high temperature and pressure gases to apply a force to certain components of the engine, e.g., piston disposed in a cylinder, to move the components over a distance. Each cylinder may include one or more valves that open and close correlative with combustion of the carbonaceous fuel. For example, an intake valve may direct an oxidizer such as air into the cylinder, which is then mixed with fuel and combusted. Combustion fluids, e.g., hot gases, may then be directed to exit the cylinder via an exhaust valve. Accordingly, the carbonaceous fuel is transformed into mechanical motion, useful in driving a load. For example, the load may be a generator that produces electric power.
In order to maximize performance, the fuel-air mixture is ignited when the piston is at a particular location in the cylinder. Unfortunately, ignition or timing of the ignition of the fuel-air mixture may become inaccurate over time. Inaccurate ignition may result in a reduction in effective expansion ratio and peak firing pressure, thereby reducing an efficiency of the engine. Alternatively, inaccurate timing of the ignition event may result in an increase in peak firing pressure resulting in other undesired conditions, such as detonation (e.g., pre-ignition, knocking, or pinging) of the fuel-air mixture in the combustion chamber, which also reduces an efficiency of the engine. Accordingly, detection of ignition accuracy in reciprocating engines is needed.